By doing this, you can’t be doing that. What is “that” worth? Hopefully less than this. Otherwise, it is costing you to do this because that is more valuable.
But if this is more valuable, then leaving that undone, unexplored, unpursued is the right thing to do. Of course, there are other considerations in pursuing that, such as whether you can pull it off or not, whether you’d be happy/fulfilled doing it, etc. etc.
But the fact remains when you could do this or that (and/or that, and/or that too), deciding is a matter of considering not only the value of what you choose, but the value of what you do not choose as well.
Always remember to spend others time wisely too!
Wow! That must mean imagination is a key to success, because without one, it’s hard to grasp this or that.